1. Field of the Invention
The present invention relates to a stop and start control method of a vehicle which performs a crank angle stop position control at the time of stopping an internal combustion engine and selects an optimal engine start method based on the state of a crank angle stop position after stopping.
2. Description of the Related Art
Recently, there is known an engine stop and start control apparatus for automatically stopping an engine when the vehicle stops and automatically restarting the engine to start the vehicle when an instruction to start is given from the stopped state, in order to reduce a fuel consumption amount and exhaust gas during idling, from the viewpoint of environmental conservation, resources and energy saving or the like.
There is also known an engine start apparatus for restarting the engine by the starter, in which the crankshaft is rotated in reverse direction, before the vehicle starts next time, to the crank angle stop position where the starting torque becomes smaller, when the starter is rotated in the normal direction during the stop control of the vehicle and the crank angle is at the crank angle stop position where the starting torque of the starter is large, in order to improve starting performance at the time of starting the engine. For example, see Japanese Patent Application Laid-Open No. 2000-283010.
In addition, for an identical purpose, there is known an engine start apparatus which performs engine restart by supplying the fuel to a cylinder in an expansion stroke and by igniting the fuel in the cylinder at the time of starting the engine, without operating the starter. For example, see Japanese Patent Application Laid-Open under No. 2002-4985.
However, in the above-described engine start apparatus, if the crank angle cannot be controlled at a desired crank angle stop position by a problem occurring to a crank angle sensor or the like, there is a possibility that the engine restart by the starter fails because the necessary starting torque of the engine becomes larger. Though the engine may be restarted by the starter when the engine restart fails, the drivability is deteriorated because the engine restart cannot be promptly performed under the condition.
Particularly, when the above-described engine restart method is applied to an economic-running vehicle or a hybrid vehicle having the engine stop and start control apparatus capable of automatically stop and start the engine, the problem of the deterioration of the drivability becomes much more serious because the engine stop and the engine start are performed frequently.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide an engine start control method which makes an engine promptly and reliably restart based on the state of a crank angle stop position after a stop control.
According to one aspect of the present invention, there is provided a stop and start control apparatus of an internal combustion engine including a stop control unit which controls a crank angle of the internal combustion engine within a range of a predetermined crank angle at a time of stopping the internal combustion engine, and a start control unit which starts the internal combustion engine by a cranking unit at a time of starting the internal combustion engine, wherein the start control unit starts the internal combustion engine by different methods when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle and when the internal combustion engine stops within the range of the predetermined crank angle.
By the above-described stop and start control apparatus of the internal combustion engine, for example, the stop control of the internal combustion engine is performed in the idling stop so that the crank angle is within a predetermined crank angle range. The predetermined crank angle range is prescribed as a crank angle range in which an energy needed to start the engine at the time of the next engine start is small. When the internal combustion engine stops within the predetermined crank angle range at the time of starting, the internal combustion engine is started by a predetermined cranking unit. However, if it is possible that the internal combustion engine does not stop within the predetermined crank angle range, the start is performed by another method which is different from the start method of the internal combustion engine by the above-described cranking unit. Thus, according to the crank angle position after the engine stop, the start of the internal combustion engine can be promptly and reliably performed by an appropriate cranking unit.
The cranking unit may be an electric motor, and the start control unit may start the internal combustion engine by applying, by the electric motor, a larger torque when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle than when the internal combustion engine stops within the range of the predetermined crank angle. When there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle, it is expected that the large torque is needed at the next time of starting. Therefore, the engine is reliably started by giving the large torque by the electric motor in that case.
The start control unit may start the internal combustion engine by a first electric motor when the internal combustion engine stops within the range of the predetermined crank angle, and by a second electric motor different from the first electric motor when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle. According to this feature, the electric motors having the large torque and having the small torque are utilized. The electric motor having the small torque is utilized when the engine stops within the range of the predetermined crank angle. The electric motor having the large torque is utilized when there is a probability that the engine does not stop within the range of the predetermined crank angle, thereby to reliably start the engine.
In a preferred embodiment, the first electric motor may be a motor generator functioning as a motor and an electric generator, and the second electric motor may be a DC starter functioning as a motor. According to this feature, the first electric motor, which functions as a motor, can also function as an electric generator. Thus, when the second electric motor functions as an electric generator, charge can be performed by supplying generated power to a power supply unit during braking, such as reducing speed of a vehicle. On the other hand, the second electric motor, which is utilized at the time of the first starting of the internal combustion engine, may be the DC starter functioning as the motor.
The start control unit may start the internal combustion engine by combusting, during an expansion stroke, a fuel supplied at the time of stopping the internal combustion engine when the internal combustion engine stops within the range of the predetermined crank angle, and the start control unit may start the internal combustion engine by the electric motor when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle. According to this feature, since the energy for starting the engine is comparatively small when the engine stops within the range of the predetermined crank angle, the internal combustion engine is started by combusting, during the expansion stroke, the fuel supplied at the time of stopping the engine. On the other hand, when there is a probability that the engine stops out of the range of the predetermined crank angle, the electric motor is used to reliably start the engine because the large torque is needed.
In a preferred example, the case when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle may be a case when an actual crank angle at the time of stopping the internal combustion engine is out of the range of the predetermined crank angle.
The actual crank angle may be outputted from the crank angle sensor detecting the crank angle of the internal combustion engine. Thus, the actual crank angle can be appropriately and reliably detected.
In another preferred example, the case when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle may include a case when an estimation accuracy of an estimating processing of the crank angle at the time of stopping the internal combustion engine is smaller than a predetermined standard.
The estimating processing may estimate the crank angle based on an output from the crank angle sensor of the internal combustion engine and rotation detecting output from the electric motor serving as the cranking unit. According to this feature, since the crank angle is estimated based on the output from the crank angle sensor and the rotation detecting output from the electric motor, the crank angle can be estimated with high accuracy. Moreover, in another example, the estimating processing may correct the rotation detecting output from the electric motor by the output from the crank angle sensor. According to this feature, the electric motor can detect the rotation output of a crankshaft with high accuracy, and at the same time, reverse rotation can also be detected. However, in the rotation detecting output from the electric motor, an accumulative error occurs due to a deviation of the belt connecting a pulley of the electric motor and the crankshaft pulley. Therefore, the amount of the accumulative error is corrected by the output from the crank angle sensor. As a result, the crank angle can be detected as an absolute angle with high accuracy.
In still another preferred example, the case when there is a probability that the internal combustion engine does not stop within the range of the predetermined crank angle may include a case when there is a probability that the crank angle changes after the stop of the internal combustion engine. In still another example, the case when there is a probability that the crank angle changes may be a case when the crank angle changes by receiving an external force after the stop of the internal combustion engine. According to this example, the case when there is a probability that the crank angle changes may be the case when the crank angle changes, e.g., the vehicle is moved due to the external force caused by the slop when the vehicle stops on the climbing lane after stopping of the internal combustion engine.
The stop control unit may automatically stop the internal combustion engine when a predetermined stop condition is satisfied, and the start control unit may automatically start the internal combustion engine when a predetermined start condition is satisfied. According to this feature, the stop and start control of the internal combustion engine according to the present invention can be preferably applied to idling stop control of a so-called economic-running vehicle or a hybrid vehicle. By this, an appropriate cranking unit can be selected in accordance with the state of the crank angle stop position after the stop control, and the internal combustion engine can be promptly and reliably started.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below.